1. Field of the Invention
This invention relates to hand tools, and more particularly to prying tools of the type used in removing headed fasteners, such as automobile panel fasteners and the like.
2. Prior Art
In modern automobiles, non-structural components, such as feature strips, decorative panels, and insulating mats, are commonly held in place by means of large-headed, plastic fasteners having serrated stems adapted for insertion into retaining openings or clips in adjacent structural members. Removal or replacement of a component is easily accomplished by merely prying the fastener out of its retainer. If undamaged, these fasteners can be used and reused a number of times.
Although no special tool is required, and indeed, virtually any screw driver, knife blade, pry-bar, diagonal cutter, or pair of pliers that can be wedged under the head of the fastener will serve the purpose, a widely recognized need exists for a specialized fastener removing tool for the automobile manufacture, repair, and upholstery trades.
A variety of prying tools have been developed in response to this need. Generally they are of two types. One type incorporates fixed "claws" or pivotably connected jaws adapted to apply leverage between the underside of the fastener head and the underlying surface. The second employs pliers-like means for gripping the stem of the fastener and applies the prying force to the stem rather than to the head of the fastener. U.S. Pat. Nos. 713,808 and 4,658,489 are illustrative of the first type of tool. Several tools of the second type are described in U.S. Pat. Nos. 832,541, 1,289,761, and 1,802,666.
Both types of prior art tools suffer from major deficiencies: In those of the first type, the prying leverage applied against the underside of the fastener head imposes substantial shear and torsional forces on and within the stem. These forces are focused primarily in the region of the stem immediately adjacent the head. Generally, internal stresses and structural anomalies induced during the fabrication of the fastener make this region particularly susceptible to such forces. Unless extreme care is taken in applying leverage to the head of the fastener, and frequently, despite the exercise of such care, the resulting abrupt shearing or bending of the stem causes the fastener to fail, leaving the mechanic with the frustrating, time-consuming task of removing the broken stem and searching for the lost head. Even if the fastener remains in tact, in most instances the prying claws or jaws of these tools leave the serrated stem badly marred and unusable.
Tools of the second type, which grip the stem, are difficult to use without cutting or at least scoring the shaft, rendering the fastener unusable or nearly certain to fail in future use.